Lomustine (CCNU) in Veterinary Oncology: Delayed-Toxicity Safety Profile

Lomustine, also called CCNU, is an oral nitrosourea chemotherapy drug used by veterinary oncologists for selected cancers. Use in dogs and cats is generally extra-label and requires a prescription, exact pharmacy product, scheduled laboratory monitoring and hazardous-drug handling.

Lomustine is lipid-soluble and interferes with DNA. Merck Veterinary Manual lists veterinary use in selected lymphoma, mast cell tumor and other cancer settings and emphasizes that marrow suppression may be delayed. Capsules must not be opened, crushed or repackaged by an owner unless a veterinary pharmacy and oncology team provide explicit safe instructions.

An oncologist may consider lomustine alone or within a protocol for a confirmed tumor with evidence supporting that choice. It is not appropriate as an unsupervised trial for a lump, and response in one tumor type does not establish benefit in another.

The plan may seek measurable disease control, remission or symptom benefit while preserving acceptable quality of life. Because toxicities can be delayed or cumulative, apparent wellness immediately after a dose does not replace scheduled monitoring.

Before and after treatment, the oncology team sets blood-count and liver-function monitoring according to the patient, product, previous exposure and protocol. The exact dispensing source matters because veterinary research has raised concerns about variable potency in some compounded oral chemotherapy products.

Merck Veterinary Manual summarizes lomustine's veterinary indications, oral route and risks including delayed myelosuppression and hepatotoxicity in dogs. UC Davis veterinary oncology reporting highlights why compounded-product potency and pharmacy selection require professional oversight.

Potential effects include nausea, vomiting, diarrhea, delayed and sometimes severe reduction in blood cells, liver injury in dogs and cumulative kidney or lung effects. Fever, marked lethargy, unusual bruising or bleeding, jaundice, repeated vomiting or diarrhea, breathing change or collapse requires prompt veterinary direction.

All other chemotherapy, marrow-suppressive drugs, liver-affecting medicines and supplements must be reviewed. Treat capsules and body waste as hazardous exactly as the dispensing clinic instructs; pregnant people and others at higher exposure risk should discuss who will handle the medication.